The invention relates to an apparatus for correcting the spacing between upper and lower dies of a press at the bottom dead center, and more particularly, to an apparatus for automatically correcting the spacing of such dies by expansion and contraction of a piezoelectric actuator.
In a press having dies, including an upper die mounted to a slide and a lower die mounted to a bolster, pressing operations are performed by moving a slide up and down using a crankshaft or the like. It is known that in such a press the spacing of the dies at bottom dead center may change due to a change in temperature. It is not acceptable to leave such a change uncorrected because the change will worsen the accuracy with which products are pressed.
A conventional approach to reducing the change in die spacing at bottom dead center is to pour oil, which is controlled at a given temperature, over the connecting rod, as disclosed in Japanese Patent Pub. No. 1-30569. Another approach is to change the rigidity of a stopper block interposed between the slide and the bolster, as disclosed in Japanese Patent Pub. No. 1-55056 and its U.S. counterpart, U.S. Pat. No. 4,377,084.
The former approach, however, requires an oil temperature controlling unit and, moreover, with this approach it is difficult to quantitatively adjust the die spacing at bottom dead center. With the latter approach, one must select a stopper block of an appropriate rigidity for the particular press load and press machine.